It has been found that roadways, bridges and the like which are frequently traveled by vehicles carrying extremely heavy loads are subject to serious damage by the passage of such vehicles. It has also been found that such damage may be limited to varying degrees by complicated distributions of the heavy loads across a large number of axles. The relationships of load and axle configuration are, in fact, subject to strict Federal and State regulation. The enforcement of the so-called "Bridge Formula" exemplifies such regulations. Because the size and weight of the loads being transported varies very greatly, it is inefficient in the trucking industry to use the same number of axles for a relative light load as would be needed with an extremely heavy load. Trailers are now available to which auxiliary axles may be added and removed to accommodate various weights and sizes of the load. The present invention is directed to a trailer assembly for transporting large heavy loads, (as well as more moderate loads) by the use of such removable auxiliary axles. More particularly, the invention involves improvements in the connections between an auxiliary or booster frame with its axles assemblies, on the one hand, and the main frame of the trailer, on the other hand, for distribution of weight from the axles supporting the main frame to one or more booster or auxiliary axles.
Trailer assemblies for transporting large, heavy loads generally include a main frame for carrying the load, a kingpin assembly for attaching the main frame to a power unit or towing vehicle to carry the front of the main frame, and a rear axle group for carrying wheels that support the rear of the main frame.
For moderate loads it is sufficient to distribute the weight of the load between the rear axle or axles of the power unit and the axle group at the rear of the trailer. For extreme loads, further distribution of the weight of the load is required. In these instances, one or more booster axles is coupled to the rear of the main frame and some of the load from the multiple axles at the rear of the trailer is distributed to these booster axles.
A number of trailer configurations which have been developed for this purpose, and some additional general background on trailer systems for extremely heavy loads are described in U.S. Pat. No. 4,423,884: Gevers "BOOSTER AXLE CONNECTION SYSTEM FOR A TRAILER ASSEMBLY" the specification which is hereby incorporated by reference. In some prior systems, the connection between the main frame and the booster axles or axles has included a booster beam and a pivot joint beneath the rear of the main frame (or a main frame extension,) pivotally connecting the main frame to the booster beam. Removal of the booster axle or axles requires disassembly of the booster beam or the main frame extension beam. In some configurations this pivot assembly results in an unusable protrusion of considerable lengths from the rear of the trailer.
In other prior configurations, for instance, where the main frame extension is removable, the process of connecting the booster assembly requires exacting alignment procedures. Most such configurations require auxiliary jacking, lifting, and blocking equipment to attach the booster assembly to the trailer main frame.
These prior configurations often resulted in main frame extensions which extend forward as well as rearwardly from the rear axle suspension system. This extension precludes the free placement of such devices as brake valves and air reservoirs which are preferably located in the general area forward of the rear axle.
These and other difficulties and disadvantages found in the prior art devices have been obviated in a novel and non-obvious manner by the devices embodying the present invention.
Therefore, it is one of the primary objects of the present invention to provide a booster axle connection design in which a main pivot between the main frame and a booster frame remains in constant connection while the load distribution is adjusted by a auxiliary link or links.
A related object is to provide a booster axle connection design in which the connection may be made and adjusted without requiring exact pre-alignment of the parts.
Another object of the invention is to provide a booster connection design that includes an adjustment provision such that the rear of the main frame can be set at various heights to compensate for variations in the deflection of the frame and suspension which results from variations in the weight of the load.
Another object of the invention is to provide a booster axle connection design which allows the addition of a third axle to a tandem axle group in such a way that the third (or booster) axle is positioned the same distance behind the last axle of the main suspension as the axles of the main suspension are from each other.
A related object is to provide a booster axle connection design in which each axle of the augmented group assumes an equal share of the payload, whether on level or uneven terrain.
A further object of the invention is to provide a booster axle connection design with the mechanisms necessary for the distribution of the weight of the payload but which is so configured to allow an unobstructed volume of space between main structural frame members in the vicinity of the first main axle, this volume being suitable for the permanent mounting of control equipment, such as brake valves and air reservoirs necessary for optimum trailer operation.
A still further object of the invention is to provide a booster axle connection system which avoids protrusion of structural members above the main frame and in the vicinity of the main axle and avoids interference with the placement of a payload on the main structural members in this vicinity.
It is also a general object of the invention to provide a booster axle connection system which is uncomplicated and rugged in construction, which can be economically manufactured, and which is capable of a long life of useful service with reasonable maintenance.
With these and other objects in view, as will be apparent to those skilled in this art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended to the specification.